RC filters are known which have a frequency-dependent filter curve. Such RC filters typically comprise an ohmic resistor and a capacitor. By suitable dimensioning of a resistance of the ohmic resistor and/or a capacitance of the capacitor, specific filter characteristics, such as in particular a specific filter curve, can be achieved. For example, a 3 dB point can be fixed.
However, such RC filters can have limitations. It may thus be possible, for example, for a finite input resistance of a load which is coupled to the RC filter as downstream stage to change the filter characteristics. Thus, in this scenario, a finite current can flow through the ohmic resistor of the RC filter in the case of a finite input resistance, which in turn causes a voltage drop across the resistor. Thus, a changed voltage drop can form across the capacitor, for example, as a result of which the filter characteristics can be changed. For example, in particular tolerances or drifts in the input resistance can have an influence on the filter characteristics in this way. The ohmic resistor can heat up.
Technologies are known for reducing such an influence of the downstream load on the RC filter. Firstly, it may be possible to use a resistor with comparatively small dimensions. In this case, the voltage which forms as a voltage drop across the ohmic resistor can be comparatively low. However, this may entail the disadvantage that it may be necessary for this purpose, in order to ensure the same filter curve of the RC filter circuit, to use a comparatively high capacitance of the capacitor. This can result in increased costs.
Technologies are also known in which an operational amplifier is used as buffer for the RC filter circuit. The operational amplifier has a comparatively high input resistance, for example in the gigaohms range. In this way, only a particularly low current can flow through the ohmic resistor of the RC filter circuit. However, such an operational amplifier often causes increased current consumption, an offset, increased signal noise, increased temperature drift and generally increased complexity.
Therefore, there is a need for improved circuits which provide a voltage filtered by an RC filter circuit to a load. In particular, there is a need for technologies which ensure stability of filter characteristics of the RC filter circuit even when there is a coupled load with a finite input resistance.